In addition to dynamic scattering mode liquid crystal devices operated using a d.c. drive or an a.c. one, the prior art also includes field effect mode liquid crystal devices which have generally been operated using an a.c. drive in order to avoid performance impairment problems associated with electrolytic degradation of the liquid crystal layer and which have employed liquid crystals that interacts with an applied electric field by way of an induced dipole. As a result such field effect devices are not sensitive to the polarity of the applied field, but respond to the applied RMS voltage averaged over approximately one response time at that voltage. There may also be frequency dependence as in the case of so-called two-frequency materials, but this only affects the type of response produced by the applied field.
In contrast, a ferroelectric liquid crystal exhibits a permanent electric dipole, and it is this permanent dipole which will interact with an applied electric field. Ferroelectric liquid crystals are of potential interest in display, switching and information processing applications because they are expected to show a greater coupling with an applied field than that typical of a liquid crystal that relies on coupling with an induced dipole, and hence ferroelectric liquid crystals are expected to show a faster response. A ferroelectric liquid crystal display mode is described for instance by N. A. Clark et al in a paper entitled 'Ferro-electric Liquid Crystal Electro-Optics Using the Surface Stabilized Structure` appearing in Mol. Cryst. Liq. Cryst. 1983 Volume 94 pages 213 to 234. By way of example reference may also be made to an alternative mode that is described in commonly assigned U.S. patent application Ser. No. 782,796, W. A. Crossland et al "Ferroelectric Liquid Crystal Display Cells" which is based on and claims priority from British Patent Application No. 8426976. To the extent the teachings of any of these related publications and applications may be useful in the understanding and use of the present invention, they are hereby incorporated by reference.